Unit 4: Maintaining life

GRADE 8 – Unit 4: Maintaining life — HIA International - Grade 8 Revision Notes & Topical Questions

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Lesson summary

GRADE 8 - Unit 4: Maintaining life — HIA INTERNATIONAL notes: Describe the characteristics of living things and viruses, classify organisms and build keys, explain water uptake and transpiration, excretion and keeping a fetus healthy.Seven characteristics — movement, respiration,…

All seven needed
Making a key
Observable feature
Root hair cells
Waxy cuticle
Need for water

Part 1 of 6Characteristics of living things

Characteristics of living things

Seven characteristics

Seven characteristics movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

Nutrition

Nutrition taking in materials for energy, growth and repair;
- plants photosynthesise and animals eat other organisms.

All seven needed

All seven needed a car moves and uses fuel, and a crystal grows, but neither shows all seven.

Viruses

Viruses very small particles seen only with an electron microscope, replicating only inside living cells.

Part 2 of 6Classification

Levels

Levels kingdom, phylum, class, order, family, genus, species.

Kingdoms

Kingdoms animals, plants, fungi, protoctists and prokaryotes (bacteria).

Species

Species a group that can reproduce together to produce fertile offspring.

Group	Body covering	Breathing	Reproduction	Example
Fish	Wet scales	Gills	Eggs in water	Salmon, shark
Amphibians	Moist skin	Gills (young), lungs and skin (adult)	Jelly eggs in water	Frog, newt
Reptiles	Dry scales	Lungs	Leathery eggs on land	Snake, lizard
Birds	Feathers	Lungs	Hard-shelled eggs	Eagle, penguin
Mammals	Hair or fur	Lungs	Live young, fed milk	Human, whale, bat

Part 3 of 6Using and making keys

Start at the first question.

Look closely at the organism and choose the answer that fits.

Follow to the next question.

Repeat until you reach a name.

Using and making keys

Making a key

Making a key list the organisms, choose one observable feature that splits them into two, write it as a yes/no question, repeat for each group and check the key works.

Observable feature

Observable feature something you can see or count, such as the number of legs.

Part 4 of 6Water uptake and transpiration

Root hair cells

Root hair cells have a long extension that absorbs water and minerals.

Xylem

Xylem carries water up the plant to the leaves.

Transpiration

Transpiration loss of water vapour from the leaves, mainly through the stomata.

Waxy cuticle

Waxy cuticle reduces water loss from the leaf.

Need for water

Need for water photosynthesis, transport, support and cooling.

Part 5 of 6Excretion and the kidneys

Excretion and the kidneys

Excretory products

Excretory products carbon dioxide, urea (from excess amino acids, removed by the kidneys) and excess water and salts.
- (from respiration, removed by the lungs)

Skin

Skin excretes some water, salts and urea in sweat.

Urinary system

Urinary system two kidneys, two ureters to the bladder and the urethra out;
- blood enters by the renal artery and leaves by the renal vein.

Filtering and reabsorption

Filtering and reabsorption small molecules are filtered out, and glucose, much water and needed salts are reabsorbed;
- the rest forms urine.

Water balance

Water balance dehydrated gives small volume of concentrated urine;
- drinking a lot gives a large volume of dilute urine.

Kidney failure

Kidney failure treated by dialysis or a transplant.

Part 6 of 6Pregnancy and the fetus

Exchange

Exchange the placenta and umbilical cord link mother and fetus;
- oxygen and nutrients pass to the fetus and carbon dioxide and urea pass back without the bloods mixing.

Diet

Diet the mother’s diet affects the fetus and needs extra protein, iron and calcium.

Harmful substances

Harmful substances smoking, alcohol and drugs can harm the fetus, and some pathogens cross the placenta.

Key terms

Term	Meaning
Organism	A living thing.
Species	A group of organisms that can reproduce together to produce fertile offspring.
Dichotomous key	A key with two choices at each step.
Transpiration	Loss of water vapour from leaves.
Xylem	Tissue that carries water up the plant.
Excretion	Getting rid of waste made in body cells.
Urea	A poisonous waste made in the liver from excess protein.
Placenta	Where substances are exchanged between mother and fetus.

Avoid these mistakes

Saying a car is living because it moves — it must show all seven characteristics.

Mixing up amphibians and reptiles — amphibians have moist skin and jelly eggs in water; reptiles have dry scales and leathery eggs on land.

Using a key question that is not observable — use features you can see or count.

Saying glucose is excreted in urine — it is reabsorbed.

Saying the maternal and fetal bloods mix — substances pass across the placenta without mixing.

Last updated: 14 October 2026